#!/usr/bin/node

const Readable = require('stream').Readable;

let c = 'a'.charCodeAt(0);//转为ASCII码


class MyReadable extends Readable{
  constructor(){
    super();
  }

  _read(){
    rs.push(String.fromCharCode(c++));
    if(c>'z'.charCodeAt(0)) rs.push(null);
  }
}

let rs = new MyReadable();

rs.pipe(process.stdout);
